The present invention relates to optical glass fibers and more particularly to the splicing or joining of two separate optical fibers in such a way as to achieve maximum light transmission.
To achieve a good splice and minimize the loss of light at the joint, which is known as "insertion loss", the two optical fibers must be accurately aligned, the fiber ends must be in proper condition for splicing and there must be accurate control of the diameters of the fibers. The most difficult parameter to control is axial alignment since even quite small misalignments will result in appreciable insertion loss.
One method employed in performing optical fiber splicing is accomplished by applying an optical adhesive material to the fiber ends, clamping the ends together in fixed alignment and curing the adhesive. In another method, the optical fibers are aligned in an axial direction and are fused together at their ends by the application of heat to the joint area.
U.S Pat. No. 3,810,803 to P. H. Buhite et al discloses inserting a quantity of thermoplastic into an electrically conductive sleeve having flared ends. The fiber ends are then inserted into the sleeve, current is applied to the sleeve to cause the thermoplastic to become molten and then the sleeve is allowed to cool. Because heat must be applied to the sleeve after the insertion of the optical fibers into the sleeve, stress is introduced into the waveguiding structures which may result in reduced light transmitting capability and eventually failure of the optical fiber itself.
Lower insertion losses can be achieved by enclosing each of the fibers in a respective ferrule and then aligning the two ferrules by locating them in a closely fitting sleeve.
U.S. Pat. No. 3,870,395 to D. Schichetanz is directed to a capillary tube having a reduced central dimension which is slightly larger than the outer diameter of the fibers to be jointed. The tube is filled with a fluid and the ends of the tube provided with caps to retain the fluid.
Such reduced central dimension used with snug-fitting sleeves usually present problems. In order to provide alignment accuracy, the diameter of the central portion or entire sleeve must be only slightly larger than that of the fiber. Therefore, circular configuration and diameter tolerances of both fiber and sleeve must be strictly controlled. Also, with a snug-fitting sleeve fiber insertion of optical fibers therein is difficult.
In an article entitled "Loose Tube Splices for Optical Fibers" by C. M. Miller, appearing in The Bell System Technical Journal, September 1975, pp 1215-1225, a loose tube splice is used. In order to improve splicing, the optical fiber ends are biased to one corner of the square cross section of the tube by bending the fibers outside of the tube. The amount of bending of each fiber outside of the tube is critical since too much or too little bending of either fiber will cause transmission loss since the planar end faces of the fibers will not be accurately aligned in the tube. Furthermore, each end of the fiber must receive the same amount of bend so that one fiber end will not be offset by even a small amount so as to cause insertion loss. This is very difficult to achieve.